The present invention relates to a spray nozzle for spraying liquids.
Such a spray nozzle is generally known in the prior art. It is used on, for example, a spray boom. European Patent Application 0,373,034 describes a method for applying a certain pattern to the ground by a series of electrically operable spray nozzles. Various other control means for controlling the passage of a fluid such as nutrients and crop protection products are known in the prior art. The simplest design is a manually operated, electrical or pneumatic valve which is fitted in the spray boom. It controls all or a number of spray nozzles. Environmental considerations and the waste involved mean that this is no longer the optimum solution. For the fact is that after such a valve has been taken into the switched-off position the downstream spray nozzles can still drip. Besides, with this design it is not possible to control the spray nozzles separately, which can be important if a piece of land extends at an angle relative to the direction of movement of the spray boom.
A first proposal for overcoming this problem is to fit a pneumatic piston-cylinder in the spray nozzle holder. In this case the piston operates a diaphragm which in the unexcited state provides for a shut-off in the passage from the supply line to the spray nozzle head in the spray nozzle holder. This means that it is possible in principle to control each spray nozzle head separately. However, there are at least two disadvantages involved in such a construction. First, the control by means of a diaphragm is relatively sluggish, which is of minor importance if large quantities of fluid have to be sprayed, but if very small quantities have to be dispensed for a short period, it does play an important role. Besides, an extremely large number of components is necessary for separate control. For such separate control will in the first instance be on the basis of electrical signals, which electrical signals have to be converted into pneumatic signals. Moreover, a separate compressor has to be fitted on the crop protection machine, or has to be present elsewhere.